1. Field of the Invention
This invention relates generally to burglar alarm and alarm systems, and relates more particularly to central station alarm systems.
2. Description of the Prior Art
Central station alarm systems are known in the art, and provide a plurality of sensing units located within their respective protected areas such as stores, banks and the like and all in communication with a central station which monitors the activities of each sensing unit during prescribed periods. The prescribed periods during which the activities of each sensing unit are monitored are typically dictated by the user, and may be considered as generally reflecting the hours of operation of the protected business.
The prescribed periods of protection are conventionally entered into a central processing device which may include a computer or similar high-level monitor. Examples of such systems are Hewitt et al U.S. Pat. No. 4,006,460 and Atkinson U.S. Pat. No. 3,697,984. Other more basic alarm systems are shown by Goldsby et al U.S. Pat. No. 3,858,181; Gall U.S. Pat. No. 3,943,492; Klein et al U.S. Pat. No. 3,803,594; Donovan U.S. Pat. No. 3,792,470; Lee U.S. Pat. No. 3,626,098; and Williams U.S. Pat. No. 3,340,362.
It has also been known in the art to employ a processing device at both the central station and each remote installation, as suggested by Wadhwani et al U.S. Pat. No. 3,925,763 and Bridge et al U.S. Pat. No. 3,454,936. Typically these satellite processing devices provide only very limited capabilities such as calling programs from the central station or encoding messages for transmission to the central station. Similarly limited functions of the remote unit are also shown in Woodward et al U.S. Pat. No. 3,839,707, which employs microprocessors at both the central and satellite stations. Bickel et al U.S. Pat. No. 3,883,695 likewise shows the use of a PROM in a satellite station, although only in combination with a timing control circuit.
Numerous difficulties have been encountered with systems of the type discussed above. Foremost among these has been the difficulty in altering the opening and closing times for a given protected area. Conventionally, and as noted above, only the central station has been able to alter the times at which the alarm system begins and ends monitoring a specific protected area. These start/stop times are generally programmed in the central station device, so that a subscriber must telephone or otherwise contact an operator at the central station each time a different start or stop time is desired. Because of the inherent error factors, and wasted time, involved in such a convoluted communications loop, such alarm systems have been unsatisfactory.
Previous systems also encountered difficulties in the event of equipment failures. In prior art systems, no means was available by which an improperly operating detection zone or device could be overriden by the user. Rather, a serviceman was required to come to the monitored location to shunt the device until repairs or other services could be made. This required additional down time of the other, properly operating detection zones, in addition to being a considerable inconvenience to the user. Thus there has been a need for a remotely accessible alarm system suitable for use as a central station device.